Unit 6: Organic Chemistry

Cover introduction, alkanes, & cycloalkanes

There will be two quizzes

Standards Covered Today:

1. Describe the features of a homologous series.

2. State names and draw structural formulas for organic compounds using the IUPAC Naming System.

3. Draw structural formulas and state names of non-cyclic (straight chain) alkanes up to C10, including isomers.

4. Draw structural formulas and state names of cyclic structures up to C10

Introduction

In all organic compounds, all carbon atoms must make four bonds, all oxygen atoms must make two bonds, all nitrogen atoms must make three bonds, all hydrogen atoms must make one bond, and all halogens must make one bond.

Names of Structures

Lewis Structures Structural Formulas Condensed Formulas &

Structures Line Structures C6H14 or CH3(CH2)4CH3

Notes on Structures

Structural Formula: shows all bonds including hydrogen

Condensed Formula: These are generally written without lines indicating bonds, or showing lone pairs, and parentheses are used for identical groups.

Line Formula: Bonds are represented by lines, carbon atoms are assumed to be present at the start and finish of a line. Nitrogen, oxygen and halogens are labeled, but hydrogens

are only shown when bonded to a drawn atom. Each atom is assumed to have sufficient hydrogen atoms

around it to make it neutral.

Isomers

Draw a structural formula for C4H10

An isomer is a compound that has the same molecular formula as another.

Structural Isomers: these are isomers that differ in their bonding sequence. They have different bond connectivity.

CH3 CH2 CH2 CH3 CH3 CH

CH3

CH3

n-butane isobutane

Introduction to Nomenclature of Organic Molecules

Four Categories: Alkanes Alkenes Alkynes Cyclic Structures

Alkanes

Alkanes are the simplest organic molecules, they only contain C and hydrogen, and only contain single bonds. Considered to be hydrocarbons

Compounds that have the maximum number of bonded hydrogens, are said to be saturated. Therefore, alkanes are the most saturated

compounds General Formula: CnH2n + 2

Nomenclature for compounds The root name of the compound is based upon the

number of carbon atoms in the longest continuous chain.

Number of C atoms Root1 Meth-

2 Eth-

3 Prop-

4 But-

5 Pent-

6 Hex-

7 Hept-

8 Oct-

9 Non-

10 Dec-

Any series that differs only by an increasing number of –CH2- groups is known as a homologous series. The individual members are said to be homologs of each other. The series must contain the same functional

group.

C C

H

C

H

HH

C

H

H

C

H

H

H

H

H

H C C

CH3

C

H

HH

C

H

H

H

H

H

H H3C C

CH3

CH3

CH3

pentaneC5H12

isopentaneC5H12

neopentaneC5H12

IUPAC Naming System: Alkanes

1) Find the longest continuous chain of carbon atoms. This is the base name of the compound.

2) Number the longest chain beginning with the end nearest a substituent.

3) Name the substituent groups attached to the longest chain as alkyl groups. Also state the location of each alkyl group according to its numbered carbon on the main chain.

4) When two or more substituents are present, list them in alphabetical order. If two or more of the same alkyl groups are present, use the prefixes di-, tri- etc. to avoid repetition.

Alkane Nomenclature Examples

1) CH2CH3

CH-CH2-CH2-CH3H3C

3-methylhexane

3-methyl hexane

• If there are two chains of equal length, choose the chain that has the highest number of substituents.

CH3

CH2HC

HC

H3C

HC

H3C HC

CH2CH3

CH3

CH3

CH3

CH2HC

HC

H3C

HC

H3C HC

CH2CH3

CH3

CH3

Numbering starts at the end nearest a substituent so that the alkyl substituents have as low numbers as possible.

CH3

CH2

HC

HC

H3C

HC

H3C HC

CH2CH3

CH3

CH3

CH3

CH2

HC

HC

H3C

HC

H3C HC

CH2CH3

CH3

CH3

Alkyl groups are named by replacing the –ane suffix of the alkane name with –yl.E.g. CH3CH3 Ethane CH3CH2- Ethyl group

CH3CH2CH3 PropaneCH3CH2CH2- Propyl group

Prefixes are used when there are more than one type of alkyl substituent. Di = 2 Tri = 3 Tetra = 4 Penta = 5

The prefixes do not count when alphabetizing.

CH3

CH2HC

HC

H3C

HC

H3C HC

CH2CH3

CH3

CH3

3-ethyl-2,4,5-trimethylheptane

Recognizing Types of Substitution

R C

H

H

R C

R

H

R C

R

R

Primary1o carbon

Secondary2o carbon

Tertiary3o carbon

Cycloalkanes

Cycloalkanes are simply alkanes that are cyclic. Just add cyclo-before their name. Notice the general formula for cycloalkanes is CnH2n

H2C CH2

H2C H2C

H2C CH2

CH2

H2C

cyclopropaneC3H6

cyclopentaneC5H10

Two simple rules of cycloalkanes

Rule A: Decide whether the cyclic or acyclic (non-cyclic) portion contains more carbons. This determines the base name. (Alkyl substituted cycloalkane or cycloalkane substituted alkane).

Rule B: Carbons are numbered to give the lowest numbers for substituted carbons.

CH3

CH

CH3

CHCH3

CH3

methylcyclopentane (1,2-dimethylpropyl)cyclohexane

Numbering starts at the most substituted carbon, and goes around in order to give the lowest numbers.

CH3

CH3

H

H3C

1,1,3-trimethylcyclopentane

1,1,3-trimethylcyclopentane

• When there are more acyclic than cyclic carbons, the cyclic part becomes a cycloalkyl substituent.

4-cyclopropyl-3-methyloctane

4-cyclopropyl-3-methyloctane

Complex Substituents

These are named as follows:

(a) The base alkyl group is numbered staring with the carbon bonded to the main chain.

(b)The substituents are listed with the appropriate numbers, and parentheses are used to separate the substituent name.

CH3

C-CH2

CH3

CH-CH3

CH3

a (1,1,3-trimethylbutyl) group

Examples

Draw structures for the following compounds:1.) 3-ethyl-3-methylpentane

2.) 3-methyl-5-propylnonane

3.) 2,2,4,4-tetramethylhexane

4.) pentylcyclohexane

5.) 2,3-dimethyl-4-propylnonane

Give the IUPAC names of the following alkanes:1.) (CH3)2CHCH2CH(C2H5)C(CH3)3

2.)

3.) (CH3CH2)3CH

4.) (CH3)2CH(CH2)3CH3

Physical Properties of Alkanes Nonpolar What type of intermolecular forces?

Since weak interactions….so low boiling point and melting point

As molecular weight increases, interactions increase

As interactions b/w molecules increase, so does the strength of the interactions….

So what conclusions can we make?

Dispersion Forces

The higher molecular weights…..

The more branches…

Leads to liquids, then solids

More compact structure, surface area decreases

Less contact between molecules, dispersion forces decrease, so lower boiling point

Try these: Arrange in increasing boiling point:

a. CH3CH2CH2CH3, CH3CH2CH2CH2CH2CH3, CH3(CH2)8CH3

b. CH3(CH2)6CH3, CH3C(CH3)2CH2CH(CH3)2,

CH3CHCH3(CH2)4CH3

c. 2-methyl butane, 2,2-dimethylpropane, pentane

Alkene and Alkyne Nomenclature Make sure you study the different functional

groups over the break (sheet of paper with table on it)

This will need to be memorized for the quiz and test.

Quiz when we get back!

Elements of Unsaturation

A saturated hydrocarbon: CnH2n+2

Each multiple bond (and each ring) decreases the number of H’s by two.

Each of these is an element of unsaturation. To calculate: find number of H’s if it were

saturated, subtract the actual number of H’s, then divide by 2.

Propose a Structure for C5H8

First calculate the number of elements of unsaturation.

Remember:A double bond is one element of

unsaturation.A ring is one element of unsaturation.A triple bond is two elements of

unsaturation.

Alkene Nomenclature

Parent is longest chain containing the double bond.

-ane changes to -ene. (or -diene, -triene) Number the chain so that the double bond

has the lowest possible number. In a ring, the double bond is assumed to be

between carbon 1 and carbon 2.

Try these:CH2 CH CH2 CH3

CH3 C

CH3

CH CH3

CH3

1-butene

2-methyl-2-butene

3-methylcyclopentene

CHCH2CH3H3C

2-(1-methyl propyl)-1,3-cyclohexadiene

3-propyl-1-heptene

Geometric Isomerism

Similar groups on same side of double bond, alkene is cis.

Similar groups on opposite sides of double bond, alkene is trans.

C CCH3

H

H

CH3CH2

C CBr

H

Br

H

trans-2-pentene cis-1,2-dibromoethene

Alkynes

Alkynes contain a triple bond. General formula is CnH2n-2

Two elements of unsaturation for each triple bond.

Alkyne Nomenclature

Find the longest chain containing the triple bond.

Change -ane ending to -yne. Number the chain, starting at the end closest

to the triple bond. Give branches or other substituents a

number to locate their position.

Try theseCH3 C CH

CH3 C C CH2 CH2 Br

CH3 CH

CH3

CH2 C C CH

CH3

CH3

propyne

5-bromo-2-pentyne

2,6-dimethyl-3-heptyne

CH2 CH CH2 CH

CH3

C CH 3-methyl-1-hexyn-5-ene

Practice Problems

Two worksheets

Agenda

Review of alkanes, alkenes, alkynes, & cyclic structures

Nomenclature of Functional Groups

Alcohols

Simple alcohols are named as derivatives of the parent alkane, using the suffix -ol, using the following simple rules:

Select the longest continuous carbon chain, containing the hydroxyl group, and derive the parent name by replacing the -e ending with -ol.

Number the carbon chain, beginning at the end nearest to the hydroxyl group.

Number the substituents and write the name, listing substituents alphabetically.

Alcohol Examples

Ether Nomenclature

Simple ethers are named either by identifying the two organic residues and adding the word ether .

CH3—O—CH3

Dimethyl ether

CH3CH2OCH2CH3

Diethyl ether

Aldehydes Nomenclature

Aldehydes are named by replacing the terminal -e of the parent alkane with the suffix -al

The parent chain selected must contain the carbonyl group.

Number the carbon chain, beginning at the end nearest to the carbonyl group.

Aldehyde Example

methanalbutanal

2-methyl butanal

Ketone Nomenclature

The suffix for ketones is -one. The parent chain selected must contain the

carbonyl group. Number the carbon chain, beginning at the

end nearest to the carbonyl group.

Ketone Examples

3-pentanone propanone

3-methyl-2-butanone

Carboxylic Acid Nomenclature

Simple carboxylic acids are named as derivatives of the parent alkane, using the suffix -oic acid

Select the longest continuous carbon chain, containing the carboxylic acid group, and derive the parent name by replacing the -e ending with -oic acid.

Number the carbon chain, beginning at the end nearest to the carboxylic acid group.

Number the substituents and write the name, listing substituents alphabetically.

Carboxylic acid substituents attached to rings are named using the suffix -carboxylic acid.

Carboxylic Acid Examples

Ester Nomenclature

Esters are named by replacing the terminal of end with the suffix -oate

The parent chain selected must contain the

Number the end of the carbon chain (after the

second O), and give it an –yl ending. Practice Problems

Amine Nomenclature

RNH2 , R2NH, R3N In amines, a nitrogen is bonded to one, two

or three carbon atoms. Practice Problems

Functional Groups as Isomers

Some functional groups can exist as isomers of each other.

Example: C4H8O2

Try the following: